39 8 SCIENCE PROGRESS. 



of the country from the Egyptian oases to Khartum. It 

 rises gradually from beneath the Cretaceous belt of the 

 oases, and forms a barren undulating plateau upon which 

 stand a number of low flat-topped or pyramidal hills. 



This, the principal area of Nubian Sandstone in Egypt, 

 extends onlv a short distance to the east of the Nile ; but 

 similar beds underlie the Cretaceous of the Wadi Araba in 

 Middle Egypt. 



The characteristic rock of the series is a dark sandstone 

 with a siliceous cement, coloured by iron and manganese. 

 It is often very hard and durable and has yielded much 

 of the stone of which the temples of Nubia and Upper 

 Egypt have been built. But the series is not so homo- 

 geneous as its name seems to imply. Lyons (16) describes 

 beds of clay in it. sometimes of considerable extent ; and 

 also deposits of iron ore. The latter contain fragments of 

 fossil wood and are believed to have been formed in marshy 

 lagoons. 



With the exception of fragments of silicified wood, 

 referred to Nicolia, Araucarioxylon and other coniferous 

 and dicotyledonous genera, fossils are extremely rare. 

 Several observers have discovered casts of shells, but they 

 are generally indeterminable. Coquand (7), however, has 

 described a specimen from Assuan which he refers to the 

 Upper Cretaceous species Ostrca Verneuili. 



Until recently this was all the pala;ontological evidence 

 that we had as to the age of the Nubian Sandstone in 

 Egypt, and it was chiefly because the sandstone is conform- 

 ably overlaid by the Upper Cretaceous that Zittel (34) 

 considered it to be of Cenomanian age. In the Wadi 

 Araba, however, in beds which were formerly referred to 

 the Nubian Sandstone, Schweinfurth has discovered a 

 fossiliferous band some distance below the Cretaceous ; 

 and from this he collected a number of fossils which 

 he at first supposed to be Devonian (25). Further 

 examination (iy) has shown the fauna to be a Carbon- 

 iferous one, and Walther has referred it to the Car- 

 boniferous Limestone (32). Among the fossils are such 

 forms as Productus semireticulatus, Streptorhynchus crenis- 



